If your install hangs with Windows 10 build 15042, here's a workaround

Windows 10 build 15042 was released to the Fast ring last Friday, it's the first Creators Update build without a watermark and expiry date. Since then, however, some people have been having trouble installing the build, not uncommon for the Insider previews. Microsoft posted a workaround to get the install completed, but it requires a bit of work, which also includes a mandatory rollback to the build you attempted to upgrade from.

The reason the install hangs is, according to Microsoft, due to one of the required install processes getting initialized but not completing or it times out, thus causing the “hang”.

However, a company representative posted workaround steps on the Community forums, and they are as follows:

Manually reboot your PC if it “hangs” at the boot logo during the first attempt to install build 15042
Allow your PC to successfully roll back to your previous OS build
Log into your PC and open a Command Prompt (Admin) window:
Note: You MUST do this in Command Prompt, NOT PowerShell!
- Click Start
- Type Command Prompt
- Right-click Command Prompt (desktop app) in the results list
- Select Run as Administrator
- Click Yes to confirm
One line at a time, paste these commands into the command prompt window.
Press enter after each line:
reg delete HKEY_LOCAL_MACHINE\system\setup\upgrade\nsimigrationroot /f

netsh int ipv6 set locality state=disabled

reg delete HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nsi\{eb004a01-9b1a-11d4-9123-0050047759bc}\28 /f
Close the Command prompt window
Reboot your PC
Re-scan for updates and re-attempt the install

Completing the above steps should allow you to proceed and install build 15042 as expected; but If you encounter any additional issues, Microsoft wants to know about it.

Source: Microsoft Community